The long-term objective of this core is to integrate transgenic technology into the realm of investigative dermatology, so that this scientific approach becomes a standard and accessible means of addressing the function of genes thought to be important in skin disease. Currently, hypotheses linking skin disease and the function of certain gene products in vivo are based on two types of observations: l) the production or unique regulation of the gene product by cultured skin- derived cells in vitro; and 2) the observation that the gene product is aberrantly expressed in diseased skin, based on analysis of a histopathological specimen derived from biopsy material. The first class of observation, though useful, is inherently flawed, since innumerable variables can intervene between in vitro culture systems and the complexity of organized tissue. The second class of observation has a distinct inherent flaw. While it does accommodate the complexity of gene regulation in organized tissue, it cannot discriminate between cause, effect and epiphenomenon, and is fundamentally a retrospective approach. A different approach is now available to complement the first two. This approach involves manipulating the mouse genome by introducing into early embryonic cells genetic constructs that result in new expression, or specific deletion, of certain genes. This prospective approach to enabling the analysis of a particular gene product in skin disease is uniquely powerful and is likely to change, in a fundamental way, how we think about skin disease.The following Specific Aims are proposed: 1. To provide a service that will micro inject pronuclei of fertilized eggs with purified DNA constructs containing genes relevant to skin disease, and implant injected cells into pseudo-pregnant recipients, towards the generation of transgenic mice. 2. To provide a service that will transfect embryonic stem cells with targeted homologous recombination vectors containing genes or gene elements relevant to skin disease, isolate successfully modified cells after drug selection, and inject such modified ES cells into blastocysts, towards the generation of targeted gene "knockout" mice. 3. To provide dedicated space for, and to subsidize per diem housing costs of, unique transgenic mice (that currently exist or will be generated in the context of the HSDRC) that display either tissue-specific overexpression or targeted deletion of genes that may be relevant to the pathogenesis of skin disease. 4. To provide education about experimental approaches involving transgenic mice that assists HSDRC investigators in asking succinct and focused experimental questions in this powerful system.